This invention relates to production of high octane fuel from naphtha by hydrocarbon cracking to produce intermediate iso-olefins and upgrading of C6+ hydrocarbons to make high octane gasoline blending components of reduced benzene content. In particular, it relates to methods and reactor systems for cracking C.sub.7 + paraffinic and naphthenic feedstocks, such as naphthenic petroleum fractions, under selective reaction conditions to produce intermediates rich in C4-C5 isoalkenes.
There has been considerable development of processes for synthesizing alkyl tertiary-alkyl ethers as octane boosters in place of conventional lead additives in gasoline. The etherification processes for the production of methyl tertiary alkyl ethers, in particular methyl t-butyl ether (MTBE) and t-amyl methyl ether (TAME) have been the focus of considerable research. It is known that isobutylene (i-butene) and other isoalkenes (branched olefins) may be reacted with methanol, ethanol, isopropanol and other lower aliphatic primary and secondary alcohols over an acidic catalyst to provide tertiary ethers. Methanol is considered the most important C.sub.1 -C.sub.4 oxygenate feedstock because of its widespread availability and low cost. Therefore, primary emphasis herein is placed on MTBE and TAME and cracking processes for making isobutylene and isoamylene reactants for etherification.
In current refining strategies naphtha reforming provides a major source of high octane gasoline containing very high aromatic levels, including benzene. In the present integrated process, the naphtha feedstock is first partially converted in a cracking reactor containing porous solid catalyst, such as medium and/or large-pore zeolite, to obtain a mixture of light C5- olefins and C6+ hydrocarbons. The iso-olefins such as iso-butene and iso-pentene are separated from the primary effluent for etherification by conventional MTBE/TAME production methods. This processing sequence produces high octane gasoline components while minimizing the overall aromatic content of gasoline pool.